Use of Rotary Cutting Elements in Downhole Milling

ABSTRACT

A milling tool includes a milling arm with a rotatable cutting element positioned on the milling arm. The rotatable cutting element may be fixed longitudinally and radially relative to a rotational axis of the rotatable cutting element in the milling arm while being rotatable about the rotational axis.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/916,883 filed Oct. 18, 2019, which is incorporated by referenceherein for all purposes.

BACKGROUND

Wellbores may be drilled into a surface location or seabed for a varietyof exploratory or extraction purposes. For example, a wellbore may bedrilled to access fluids, such as liquid and gaseous hydrocarbons,stored in subterranean formations and to extract the fluids from theformations. Wellbores used to produce or extract fluids may be linedwith casing around the walls of the wellbore. A variety of drillingmethods may be utilized depending partly on the characteristics of theformation through which the wellbore is drilled.

Some wellbores are reinforced with casing while drilling to stabilizethe wellbore. Conventional casing is a steel or other metallic cylinderthat provides a durable surface for the interior of the wellbore. Thecasing allows downhole tools to be tripped into the wellbore with littleor no damage to the integrity of the wellbore. The outer diameter of thecasing is smaller than the drilled diameter of the initial wellbore,leaving an annular space around the casing and between the casing andwellbore. The annular space is filled with cement or other fluid thatcan harden and retain the casing in place relative to the wellbore.

The cement is pumped to the bottom of the casing and allowed to flow upthe annular space. Filling the annular space from the bottom displacesother material from the annular space and provides more complete fillingof the annular space than other delivery methods.

During creation, maintenance, and closing of a wellbore, variousmaterials may be removed by a downhole tool to extend, widen, orredirect the wellbore. For example, downhole tools remove earthenmaterial to extend the wellbore. Downhole tools are also used to removeportions of the metal casing and cement to widen the wellbore or to opena window in the casing to kick off a lateral borehole from the wellbore.

When removing material in a downhole environment, the cuttings areremoved by flushing the cuttings upward through the annular space aroundthe downhole tool with drilling fluid. Smaller cuttings are carried awayby the drilling fluid more reliably and safely than larger cuttings.

SUMMARY

In some embodiments, a downhole tool includes a milling arm and arotatable cutting element positioned in the milling arm. The rotatablecutting element is rotatable within the milling arm about a rotationalaxis of the rotatable cutting element.

In other embodiments, a milling tool includes a milling tool body and aplurality of milling arms. The plurality of milling arms projectradially from the body and are configured to move around the millingtool body in a cutting direction. At least one of the milling armsincludes a rotatable cutting element and a fixed cutting element. Therotatable cutting element is positioned in arm body of the milling armand is rotatable about a rotational axis within the arm body. The fixedcutting element is positioned in the arm body of the milling arm.

In yet other embodiments, a milling tool includes a milling tool bodyand a plurality of milling arms. The plurality of milling arms projectradially from the body and are configured to move around the millingtool body in a cutting direction. At least one of the milling armsincludes a rotatable cutting element, an inside fixed cutting element,and an outside fixed cutting element. The rotatable cutting elementpositioned in arm body of the milling arm and is rotatable about arotational axis within the arm body. The inside fixed cutting element isfixed in the arm body in a downhole direction of the rotatable cuttingelement. The outside fixed cutting element is fixed relative to the armbody and positioned radially outside of the at least one inside cuttingelement with a sacrificial region positioned therebetween.

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

Additional features and advantages of embodiments of the disclosure willbe set forth in the description which follows, and in part will beobvious from the description, or may be learned by the practice of suchembodiments. The features and advantages of such embodiments may berealized and obtained by means of the instruments and combinationsparticularly pointed out in the appended claims. These and otherfeatures will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of suchembodiments as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otherfeatures of the disclosure can be obtained, a more particulardescription will be rendered by reference to specific embodimentsthereof which are illustrated in the appended drawings. For betterunderstanding, the like elements have been designated by like referencenumbers throughout the various accompanying figures. While some of thedrawings may be schematic or exaggerated representations of concepts, atleast some of the drawings may be drawn to scale. Understanding that thedrawings depict some example embodiments, the embodiments will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is a schematic representation of an embodiment of a drillingsystem, according to at least one embodiment of the present disclosure;

FIG. 2 is a detail view of the embodiment of a milling tool with arotatable cutting element, according to at least one embodiment of thepresent disclosure;

FIG. 3 is a front view of another embodiment of a milling arm with arotatable cutting element, according to at least one embodiment of thepresent disclosure;

FIG. 4 is a radial end view of the embodiment of a milling arm of FIG.3, according to at least one embodiment of the present disclosure;

FIG. 5 is a bottom view of the embodiment of a milling arm of FIG. 3,according to at least one embodiment of the present disclosure;

FIG. 6 is a side cross-sectional view of an embodiment of a rotatablecutting element in a housing, according to at least one embodiment ofthe present disclosure;

FIG. 7 is a side cross-sectional view of another embodiment of arotatable cutting element in a housing, according to at least oneembodiment of the present disclosure;

FIG. 8 is a front view of an embodiment of a rotatable cutting elementwith an annular cutting portion, according to at least one embodiment ofthe present disclosure;

FIG. 9 is a front view of another embodiment of a rotatable cuttingelement with a plurality of cutting portions, according to at least oneembodiment of the present disclosure;

FIG. 10 is a side cross-sectional view of an embodiment of a profile ofa cutting portion, according to at least one embodiment of the presentdisclosure;

FIG. 11 is a side cross-sectional view of another embodiment of aprofile of a cutting portion, according to at least one embodiment ofthe present disclosure;

FIG. 12 is a side cross-sectional view of yet another embodiment of aprofile of a cutting portion, according to at least one embodiment ofthe present disclosure; and

FIG. 13 is a front view of an embodiment of a cutting portion with arotational chipbreaking feature, according to at least one embodiment ofthe present disclosure.

DETAILED DESCRIPTION

This disclosure generally relates to devices, systems, and methods forimproving cutting efficiency in a downhole environment. Moreparticularly, the present disclosure relates to embodiments of millingtools having a rotatable cutting element to distribute wear over theentire edge of the cutting element. Distributing wear on the cuttingelement may increase a rate of penetration of the tool, reduce thelikelihood of a cutting element and/or a tool body failure, orcombinations thereof. While a milling bit for cutting through wellborecasing is described herein, it should be understood that the presentdisclosure may be applicable to other cutting bits such as reamers, holeopeners, and other cutting bits, and through other materials, such ascement, concrete, metal, or formations including such materials.

FIG. 1 shows one example of a drilling system 100 for drilling an earthformation 101 to form a wellbore 102. The drilling system 100 includes adrill rig 103 used to turn a tool assembly 104 which extends downwardinto the wellbore 102. In the embodiment depicted in FIG. 1, the toolassembly 104 is removing a casing 107 of the wellbore 102, for example,to extend or widen the wellbore 102, or to kick off a lateral boreholefrom the wellbore 102. The tool assembly 104 may include a drill string105, a bottomhole assembly (“BHA”) 106, a milling tool 110, orcombinations thereof. In the depicted embodiment, a milling tool 110 isattached to the downhole end of drill string 105.

The drill string 105 may include several joints of drill pipe 108 aconnected end-to-end through tool joints 109. The drill string 105transmits drilling fluid through a central bore and transmits rotationalpower from the drill rig 103 to the BHA 106. In some embodiments, thedrill string 105 may further include additional components such as subs,pup joints, etc. The drill pipe 108 provides a hydraulic passage throughwhich drilling fluid is pumped from the surface. The drilling fluid maydischarge through one or more orifices in the tool assembly 104 for thepurposes of cooling the milling tool 110 and cutting structures thereon,and for lifting cuttings out of the wellbore 102 as it the casing 107 ismilled.

In general, the drilling system 100 may include other drillingcomponents and accessories, such as special valves (e.g., kelly cocks,blowout preventers, and safety valves). Additional components includedin the drilling system 100 may be considered a part of the drilling toolassembly 104, the drill string 105, or a part of the BHA 106 dependingon their locations in the drilling system 100.

In some embodiments, the BHA 106 may further include any type of bitsuitable for degrading downhole materials. For instance, the bit may bea drill bit suitable for drilling the earth formation 101. In thedepicted embodiment, the BHA 106 may include a milling tool 110 to millinto the casing 107 lining the wellbore 102 and a bit may then start alateral borehole in the earth formation 101. The milling tool 110 mayalso be a junk mill used to mill away tools, plugs, cement, othermaterials within the wellbore 102, or combinations thereof. Swarf orother cuttings formed by use of the milling tool 110 may be lifted tosurface, or may be allowed to fall downhole.

As shown in FIG. 1, the milling tool 110 may have a plurality of millingarms that are deployable from a body of the milling tool 110 to removematerial from the casing 107 and/or earth formation 101 to expand thewellbore 102.

FIG. 2 illustrates an embodiment of a milling arm 112 deployed from thebody of the milling tool 110. In some embodiments, the milling arm 112may have an arm body that is oriented in a cutting direction of themilling arm 112 around the body of the milling tool 110. The arm body114 may have one or more features thereon to remove material from aformation 101 and/or casing 107 as the milling arm 112 and milling tool110 rotates relative to the formation 101 and/or casing 107. While oneor more embodiments of a milling arm will be described in relation tomilling a casing in a downhole direction, it should be understood thatat least one of embodiments described herein may be inverted and used inan uphole milling direction. Any directional references, such asdownhole, uphole, etc., should be understood to be in reference to adownhole milling direction.

In some embodiments, a milling arm 112 may include a rotatable cuttingelement 116 located on the arm body 114. In other embodiments, a millingarm 112 may include and inside cutting element 118. The rotatablecutting element 116 may be positioned on the arm body of the milling arm112 to contact an end of the casing 107 and mill casing 107 materialwhile the inside cutting element 118 may be positioned on the millingarm 112 to remove material from an inside surface of the formation 101and/or casing 107 and/or protect the milling arm 112 from erosion and/ordamage from contact with the formation 101 and/or casing 107.

In some embodiments, at least a portion of the rotatable cutting element116 may be an ultrahard material. As used herein, the term “ultrahard”is understood to refer to those materials known in the art to have agrain hardness of about 1,500 HV (Vickers hardness in kg/mm²) orgreater. Such ultra-hard materials can include those capable ofdemonstrating physical stability at temperatures above about 750° C.,and for certain applications above about 1,000° C., that are formed fromconsolidated materials. Such ultrahard materials can include but are notlimited to diamond or polycrystalline diamond (PCD) including leachedmetal catalyst PCD, non-metal catalyst PCD, binderless PCD,nanopolycrystalline diamond (NPD), or hexagonal diamond (Lonsdaleite);cubic boron nitride (cBN); polycrystalline cBN (PcBN); Q-carbon;binderless PcBN; diamond-like carbon; boron suboxide; aluminum manganeseboride; metal borides; boron carbon nitride; and other materials in theboron-nitrogen-carbon-oxygen system which have shown hardness valuesabove 1,500 HV, as well as combinations of the above materials. In atleast one embodiment, a portion of the rotatable cutting element 116 maybe a monolithic carbonate PCD. For example, a portion of the rotatablecutting element 116 may consist of a PCD compact without an attachedsubstrate or metal catalyst phase. In some embodiments, the ultrahardmaterial may have a hardness values above 3,000 HV. In otherembodiments, the ultrahard material may have a hardness value above4,000 HV. In yet other embodiments, the ultrahard material may have ahardness value greater than 80 HRa (Rockwell hardness A).

In some embodiments, the rotatable cutting element 116 may rotaterelative to the milling arm 112 and the inside cutting element 118 maybe fixed relative to the milling arm 112. The rotatable cutting element116 may rotate relative to the milling arm 112 due at least partially tothe contact between the rotatable cutting element 116 and the formation101 and/or casing 107. For example, the rotatable cutting element 116may be oriented in the milling arm 112 relative to the direction ofmovement of the milling arm 112 to contact the casing 107 askew, therebydriving a net torque on the rotatable cutting element 116. The rotationof the rotatable cutting element 116 may limit and/or prevent excessivewear on one location of the rotatable cutting element 116 relative toother portions of the rotatable cutting element 116. In other words, therotation of the rotatable cutting element 116 allows exposure of a “new”portion of the rotatable cutting element 116 to wear the rotatablecutting element 116 evenly during use to increase the operationallifetime of the milling tool 110.

FIG. 3 illustrates another embodiment of a milling arm 212 according tothe present disclosure. The milling arm 212 may have an arm body 214similar to that described in relation to FIG. 2, with a rotatablecutting element 216 positioned thereon. In some embodiments, the millingarm 212 may include at least one inside cutting element 218 and at leastone outside cutting element 220. As described in relation to FIG. 2, theinside cutting element 218 may be positioned on the milling arm 212 in adownhole direction relative to the rotatable cutting element 216 toremove material from an inside surface of the casing and/or protect themilling arm 212 from erosion and/or damage from contact with theformation and/or casing.

In some embodiments, the outside cutting element(s) 220 may bepositioned on the milling arm 212 in a downhole direction relative tothe rotatable cutting element 216 to remove material from the formationand/or an outside surface of casing and/or protect the milling arm 212from erosion and/or damage from contact with the formation and/orcasing. In other embodiments, the outside cutting elements 220 may bepositioned at a radial end of the milling arm 212 and configured toremove at least a portion of the cement radially outside the casing thatholds the casing in position in the wellbore.

In some embodiments, the inside cutting elements 218 and/or the outsidecutting elements 220 may include an ultrahard material. In otherembodiments, the inside cutting elements 218 and/or the outside cuttingelements 220 may include a material having a higher hardness than theconstituent material of the arm body 214. For example, the insidecutting elements 218 and/or the outside cutting elements 220 may includea tungsten carbide and the arm body 214 may include a steel alloy. Inother embodiments, the inside cutting elements 218 and/or the outsidecutting elements 220 may include a PCD and the arm body 214 may includea titanium alloy.

In some embodiments, the milling arm 212 may include a sacrificialregion 219 positioned downhole of the rotatable cutting element 216. Insome embodiments, the sacrificial region 219 may be positioned adjacentto an inside cutting element 218. In other embodiments, the sacrificialregion 219 may be positioned adjacent to an outside cutting element 218.In yet other embodiments, the sacrificial region 219 may be positionedadjacent to and between an inside cutting element 218 and an outsidecutting element 220.

In some embodiments, the sacrificial region 219 may be a differentmaterial from the remainder of the arm body 214. For example, thesacrificial region 219 may include an aluminum alloy and the remainderof the arm body 214 may include a steel alloy. In other examples, thesacrificial region 219 may include a soft steel alloy and the remainderof the milling arm may include a tool steel. In at least one example,the sacrificial region 219 may include a softer material than theremainder of the milling arm 212 such that the sacrificial region 219preferentially wears in contact with the casing and/or formation tocreate a channel that may direct the casing to the rotatable cuttingelement 216.

FIG. 4 illustrates the embodiment of a milling arm 212 of FIG. 3 in anend view. In some embodiments, the rotatable cutting element 216 mayrotate relative to the arm body 214 about a rotational axis 222 of therotatable cutting element 216.

The milling arm 212 may be moved in a cutting direction 224 by the bodyof the milling tool (such as milling tool 110 of FIG. 2) to move aroundthe edge of the wellbore as the milling tool advances longitudinallythrough the wellbore. In some embodiments, the rotational axis 222 maybe oriented with a declination 226 (e.g., oriented in a downholedirection relative to the cutting direction 224. In some embodiments,the declination 226 may be in a range having an upper value, a lowervalue, or upper and lower values including any of 0°, 5°, 10°, 15°, 20°,25°, 30°, 35°, 40°, 45°, or any values therebetween. For example, therotational axis 222 of the rotatable cutting element 216 may be orientedwith a declination 226 of greater than 0° relative to the cuttingdirection 224. In other examples, the rotational axis 222 may beoriented with a declination of less than 45° relative to the cuttingdirection 224. In yet other examples, the declination 226 may be between5° and 40°. In further examples, the declination 226 may be between 10°and 35°.

FIG. 5 is a bottom view illustrating the perpendicular orientation ofthe rotatable cutting element 216 relative to the cutting direction 224of the arm body 214 during milling operations. In some embodiments, therotatable cutting element 216 may be oriented in a radially outwarddirection (e.g., away from the arm body 214) an radial angle 228 in arange having an upper value, a lower value, or upper and lower valuesincluding any of 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, or anyvalues therebetween. For example, the rotational axis 222 of therotatable cutting element 216 may be oriented radially outward at aradial angle 228 of greater than 0° relative to the cutting direction224. In other examples, the rotational axis 222 may be oriented radiallyoutward at a radial angle 228 of less than 45° relative to the cuttingdirection 224. In yet other examples, the radial angle 228 may bebetween 5° and 40°. In further examples, the radial angle 228 may bebetween 10° and 35°.

In some embodiments, the rotational rate of the rotatable cuttingelement 216 about the rotational axis 222 may be related to thedeclination 226 and/or the radial angle 228 in the radial direction. Forexample, contacting the casing with the rotatable cutting element 216with a rotational axis 222 parallel to the cutting direction 224 of themilling arm about the milling tool may result in little to no rotationof the rotatable cutting element 216. In other embodiments, a rotationalaxis 222 with a 30° declination (such as declination 226 in FIG. 4) anda 30° radial angle 228 in the radial direction may result in one or morerevolutions of the rotatable cutting element 216 about the rotationalaxis 222 for each rotation of the milling tool about the wellbore.

In some embodiments, an arm body 214 may have a bottom surface 230 thatis tapered toward rotatable cutting element 216 to provide clearance forthe rotatable cutting element 216 to contact the casing and/orformation. For example, the bottom surface 230 may have less area thanan opposite top surface to accommodate the declination of the rotatablecutting element 216. In other examples, the bottom surface 230 may haveless area than an opposite top surface to provide clearance for cuttingsor other debris to be flushed from the cutting area.

FIG. 6 and FIG. 7 illustrate different embodiments of retentionmechanisms for retaining the rotatable cutting element in a milling armwhile allowing rotation of the rotatable cutting element within the armbody. FIG. 6 is a cross-sectional view of an embodiment of a rotatablecutting element 316 inside a housing 336. In some embodiments, thehousing 336 may be an arm body (such as the arm body 114, 214 describedin relation to FIG. 2 through 5). In other embodiments, the housing 336may be a discrete part that may be fixed to the arm body. For example,the housing 336 may be fixed to the arm body by welding, brazing,adhesive, mechanical interlock, friction fit, snap fit, one or moremechanical fasteners (e.g., pins, clips, clamps, bolts, etc.), orcombinations thereof.

In some embodiments, the rotatable cutting element 316 may include acutting portion 332 and a base 334. In some embodiments, the base 334may be substantially cylindrical and received within a complimentarilysized space in the housing 336. For example, the base 334 may beconfigured to rotate freely within the housing 336 about the rotationalaxis 322.

In some embodiments, the cutting portion 332 may be integrally formedwith the base 334. For example, the cutting portion 332 may be sinteredwith the base 334, such that the cutting portion 332 and base 334 arebonded together microstructurally. In other embodiments, the cuttingportion 332 may be affixed to the base 334 by brazing, adhesive,mechanical interlock, friction fit, snap fit, one or more mechanicalfasteners (e.g., pins, clips, clamps, bolts, etc.), or combinationsthereof.

In some embodiments, at least a portion of the rotatable cutting element316 may be positioned inside the housing 336. The rotatable cuttingelement 316 may be rotatable relative to the housing 336 while beinglongitudinally fixed relative to the housing 336. For example, themovement of the rotatable cutting element 316 in the direction of therotational axis 322 may be limited and/or prevented by a retentionmember.

In some embodiments, the retention member may be an expansion ring 338.For example, the expansion ring 338 may be positioned in acircumferential groove 340 about the base 334, as the base 334 isinserted into the housing 336. The expansion ring 338 may expand uponreaching a notch 342 or shoulder in the housing 336, limiting thelongitudinal movement of the rotatable cutting element 316 relative tothe housing 336. In other embodiments, the retention member may becompression ring that is snapped around the base 334 and into the groove340 from the rear of the housing 336.

In other embodiments, the rotatable cutting element may be retained inthe housing by a plurality of retention members. FIG. 7 illustrates anembodiment of a rotatable cutting element 416 in a housing 436 with atleast part of the housing 436 positioned in the rotatable cuttingelement 416. For example, the rotatable cutting element 416 may have acutting portion 432 and a base 434, and at least a portion of thehousing 436 may protrude into the base 434. The housing 436 and base 434may have a plurality of fasteners, such as pins 444, inserted between.

In some embodiments, the base 434 may have a circumferential groove 446therein, which may receive the plurality of pins 444. The pins 444 maybe positioned in the groove 446 adjacent to the base 434 to limit and/orprevent longitudinal movement of the rotatable cutting element 416 inthe direction of the rotational axis 422. In some embodiments, the pins444 may further limit the movement of the rotatable cutting element 416perpendicular to the rotational axis 422 without inhibiting therotational movement of the rotatable cutting element 416. In someembodiments, the pins 444 may be removed from the housing 436 to allowremoval and/or replacement of the rotatable cutting element 416 forrepair of the rotatable cutting element 416 and/or a milling arm.

FIG. 6 and FIG. 7 illustrate embodiments of a rotatable cutting element316, 416 including a cutting portion 332, 432 that may be a monolithicdisc that is continuous about a circumferential edge. FIG. 8 is an endview of a front face of another embodiment of a rotatable cuttingelement 516 with a cutting portion with a continuous circumferentialedge. In some embodiments, the cutting portion 532 of a rotatablecutting element 516 may positioned at the edge of the front faceannularly about the rotational axis 522 of the rotatable cutting element516. For example, the cutting portion 532 may be an annular disc aroundthe base 534 in the center of the rotatable cutting element 516.

In some embodiments, the cutting portion 532 may be a percentage of thesurface area of the front face shown of the rotatable cutting element516 in a range having an upper value, a lower value, or upper and lowervalues including any of 5%, 10%, 15%, 20%, 25%, 50%, 75%, 80%, 85%, 90%,95%, 100%, or any values therebetween. For example, the cutting portion532 may be greater than 5% of the surface area of the front face of therotatable cutting element 516. In other examples, the cutting portion532 may be less than 100% of the surface area of the front face of therotatable cutting element 516. In yet other examples, the cuttingportion 532 may be between 10% and 60% of the surface area of the frontface of the rotatable cutting element 516. In further examples, thecutting portion 532 may be between 15% and 50% of the surface area ofthe front face of the rotatable cutting element 516.

In some embodiments, the cutting portion 532 may have a width that is apercentage of the radius of the rotatable cutting element 516 in a rangehaving an upper value, a lower value, or upper and lower valuesincluding any of 5%, 10%, 15%, 20%, 25%, 50%, 75%, 80%, 85%, 90%, 95%,100%, or any values therebetween. For example, the cutting portion 532may be an annulus with a width that is greater than 5% of the radius ofthe rotatable cutting element 516. In other examples, the cuttingportion 532 may be an annulus with a width that is between 5% and 95% ofthe radius of the rotatable cutting element 516. In yet other examples,the cutting portion 532 may be an annulus with a width that is between10% and 60% of the radius of the rotatable cutting element 516. Infurther examples, the cutting portion 532 may be an annulus with a widththat is between 15% and 40% of the radius of the rotatable cuttingelement 516.

FIG. 9 is an end view of yet another embodiment of a rotatable cuttingelement 616. The rotatable cutting element 616 may have a plurality ofcutting portions 632 affixed to a base 634. In some embodiments, therotatable cutting element 616 may have a plurality of cutting portions632 that are spaced circumferentially around the rotatable cuttingelement 616 at equal angular intervals around the rotational axis 622.In other embodiments, the rotatable cutting element 616 may have aplurality of cutting portions 632 positioned at unequal angularintervals around the rotational axis 622. In some embodiments, at leastone of the cutting portions 632 may be removable and/or replaceable tofacilitate repair of a part of the rotatable cutting element 616 withouthaving to replace the entire rotatable cutting element 616.

FIG. 10 through FIG. 12 are cross-sectional views of various embodimentsof profiles of rotatable cutting elements 716, 816, 916. FIG. 10 is aside cross-sectional view of an embodiment of a rotatable cuttingelement 716 with a cutting portion 732 fixed to a base 734. The cuttingportion 732 may have a bevel 748 located at the edge of the cuttingportion 732. In some embodiments, the bevel 748 may reduce fracturing ofthe cutting portion 732 near the edge. In other embodiments, the bevel748 may correspond to the declination and/or radial angle (such asdeclination 226 and radial angle 228 described in relation to FIG. 4 andFIG. 5, respectively) to allow the bevel 748 to contact flush againstthe casing being milled. For example, the bevel 748 may be acomplementary angle to the declination (such as declination 226described in relation to FIG. 4). In other examples, the bevel 748 maybe a complimentary angle to the radial angle (such as radial angle 228described in relation to FIG. 5).

In some embodiments, the bevel 748 may be in a range having an uppervalue, a lower value, or upper and lower values including any of 0°, 5°,10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°,80°, 85°, 90°, or any values therebetween. For example, the bevel 748may be greater than 0°. In other examples, the bevel 748 may be lessthan 90°. In yet other examples, the bevel 748 may be between 5° and85°. In further examples, the bevel 748 may be between 10° and 80°.

FIG. 11 is a side cross-sectional view of another embodiment of aprofile of a rotatable cutting element 816 with a cutting portion 832fixed to a base 834. The cutting portion 832 may have a first bevel 848located at the edge of the cutting portion 832 and a second bevel 850inward of the first bevel 848. In some embodiments, the combination ofthe first bevel 848 and second bevel 850 may reduce fracturing of thecutting portion 832 near the edge. In other embodiments, the first bevel848 may correspond to the declination and/or angle (such as declination226 and radial angle 228 described in relation to FIG. 4 and FIG. 5,respectively) to allow the first bevel 848 to contact flush against thecasing being milled. In some embodiments, the first bevel 848 may be ina range having an upper value, a lower value, or upper and lower valuesincluding any of 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, or anyvalues therebetween. For example, the first bevel 848 may be greaterthan 0°. In other examples, the first bevel 848 may be less than 45°. Inyet other examples, the first bevel 848 may be between 5° and 40°. Infurther examples, the first bevel 848 may be between 10° and 35°.

In some embodiments, the second bevel 850 may be higher than the firstbevel 848 and may be in a range having an upper value, a lower value, orupper and lower values including any of 10°, 15°, 20°, 25°, 30°, 35°,40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, or any valuestherebetween. For example, the first bevel 848 may be greater than 10°.In other examples, the first bevel 848 may be less than 85°. In yetother examples, the first bevel 848 may be between 15° and 80°. Infurther examples, the first bevel 848 may be between 45° and 80°.

In some embodiments, a rotatable cutting element may have one or morechipbreaking features on a surface thereof. For example, FIG. 12illustrates an embodiment of a rotatable cutting element 916 with abevel 948 and a chipbreaking feature 952 in a cutting portion 932. Thecutting portion 932 is fixed to a base 934. In some embodiments, thechipbreaking feature 952 may be configured to break the cutting of thecasing by bending and/or work hardening the cutting. The cutting may,therefore, break into a series of smaller pieces that are more easilyflushed away.

In some embodiments, the chipbreaking feature 952 may be a concavefeature in the cutting portion 932 that will bend the cutting formed bythe cutting portion 932. For example, the cutting portion 932 may cutmaterial from a casing at a point on the cutting portion 932 between thechipbreaking feature 952 and the bevel 948, urging material from thecasing toward the chipbreaking feature 952. The chipbreaking feature 952may then direct the cutting along the concave surface of thechipbreaking feature to fracture the cutting.

In other embodiments, a chipbreaking feature may include one or morefacets or angles to promote the fracturing of the cuttings into smallerpieces. FIG. 13 illustrates another embodiment of a rotatable cuttingelement 1016 with a faceted cutting portion 1032 within a bevel 1048 atthe edge. In some embodiments, the chipbreaking feature 1052 may includea plurality of facets which, when the rotatable cutting element 1016rotates, may interact to deflect and/or bend a cutting in a plurality ofdirections to work harden and/or break the cutting into smaller pieces.For example, a faceted chipbreaking feature 1052 may include a pluralityof ridges 1054 angularly spaced about the cutting portion 1032. Theplurality of ridges 1054 may rotationally separate concave chipbreakingfeatures 1052, similar to the concave chipbreaking features 952described in relation to FIG. 12.

In at least one embodiment, a milling arm with a rotatable cuttingelement therein may allow for longer operational lifetimes and/or moreefficient cutting of casing by distributing wear across a rotationaledge of the rotatable cutting element. The rotation of the rotatablecutting element may provide a greater wear area, increasing the cuttingefficiency of the cutting element compared to a conventional fixedcutting element. In at least one other embodiment, the rotatable cuttingelement may include a chipbreaking feature, and the rotation of therotatable cutting element may assist in breaking chips of the cutting.

The embodiments of milling arms have been primarily described withreference to wellbore milling operations; the milling arms describedherein may be used in applications other than the milling of a wellbore.In other embodiments, milling arms according to the present disclosuremay be used outside a wellbore or other downhole environment used forthe exploration or production of natural resources. For instance,milling arms of the present disclosure may be used in a borehole usedfor placement of utility lines. Accordingly, the terms “wellbore,”“borehole” and the like should not be interpreted to limit tools,systems, assemblies, or methods of the present disclosure to anyparticular industry, field, or environment.

One or more specific embodiments of the present disclosure are describedherein. These described embodiments are examples of the presentlydisclosed techniques. Additionally, in an effort to provide a concisedescription of these embodiments, not all features of an actualembodiment may be described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerous embodiment-specificdecisions will be made to achieve the developers' specific goals, suchas compliance with system-related and business-related constraints,which may vary from one embodiment to another. Moreover, it should beappreciated that such a development effort might be complex and timeconsuming, but would nevertheless be a routine undertaking of design,fabrication, and manufacture for those of ordinary skill having thebenefit of this disclosure.

The articles “a,” “an,” and “the” are intended to mean that there areone or more of the elements in the preceding descriptions. The terms“comprising,” “including,” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. Additionally, it should be understood that references to “oneembodiment” or “an embodiment” of the present disclosure are notintended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. For example, anyelement described in relation to an embodiment herein may be combinablewith any element of any other embodiment described herein. Numbers,percentages, ratios, or other values stated herein are intended toinclude that value, and also other values that are “about” or“approximately” the stated value, as would be appreciated by one ofordinary skill in the art encompassed by embodiments of the presentdisclosure. A stated value should therefore be interpreted broadlyenough to encompass values that are at least close enough to the statedvalue to perform a desired function or achieve a desired result. Thestated values include at least the variation to be expected in asuitable manufacturing or production process, and may include valuesthat are within 5%, within 1%, within 0.1%, or within 0.01% of a statedvalue.

A person having ordinary skill in the art should realize in view of thepresent disclosure that equivalent constructions do not depart from thespirit and scope of the present disclosure, and that various changes,substitutions, and alterations may be made to embodiments disclosedherein without departing from the spirit and scope of the presentdisclosure. Equivalent constructions, including functional“means-plus-function” clauses are intended to cover the structuresdescribed herein as performing the recited function, including bothstructural equivalents that operate in the same manner, and equivalentstructures that provide the same function. It is the express intentionof the applicant not to invoke means-plus-function or other functionalclaiming for any claim except for those in which the words ‘means for’appear together with an associated function. Each addition, deletion,and modification to the embodiments that falls within the meaning andscope of the claims is to be embraced by the claims.

The terms “approximately,” “about,” and “substantially” as used hereinrepresent an amount close to the stated amount that still performs adesired function or achieves a desired result. For example, the terms“approximately,” “about,” and “substantially” may refer to an amountthat is within less than 5% of, within less than 1% of, within less than0.1% of, and within less than 0.01% of a stated amount. Further, itshould be understood that any directions or reference frames in thepreceding description are merely relative directions or movements. Forexample, any references to “up” and “down” or “above” or “below” aremerely descriptive of the relative position or movement of the relatedelements.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered as illustrative and not restrictive. The scope ofthe disclosure is, therefore, indicated by the appended claims ratherthan by the foregoing description. Changes that come within the meaningand range of equivalency of the claims are to be embraced within theirscope.

What is claimed is:
 1. A downhole tool, the downhole tool comprising: amilling arm, and a rotatable cutting element positioned in the millingarm and rotatable within the milling arm about a rotational axis.
 2. Thedownhole tool of claim 1, further comprising at least one inside cuttingelement positioned in the milling arm in a downhole direction of therotatable cutting element.
 3. The downhole tool of claim 2, furthercomprising at least one outside cutting element positioned in themilling arm in a downhole direction of the rotatable cutting element. 4.The downhole tool of claim 3, the milling arm having a sacrificialregion between the at least one inside cutting element and the at leastone outside cutting element.
 5. The downhole tool of claim 1, therotatable cutting element having a front face including a cuttingportion including an ultrahard material.
 6. The downhole tool of claim5, less than 50% of the front face being the ultrahard material.
 7. Thedownhole tool of claim 5, the ultrahard material being a continuouscircumferential edge of the rotatable cutting element.
 8. The downholetool of claim 5, the rotatable cutting element have a chipbreakingfeature on the front face.
 9. The downhole tool of claim 1, therotatable cutting element being retained in a housing by one or morefasteners.
 10. The downhole tool of claim 9, wherein at least a portionof the housing is positioned within the rotatable cutting element. 11.The downhole tool of claim 1, the rotatable cutting element beingretained in a housing by at least one ring.
 12. A milling tool, themilling device comprising: a milling tool body; and a plurality ofmilling arms projecting radially from the body and configured to moveabout the milling tool body in a cutting direction, at least one millingarm of the plurality of milling arms including, a rotatable cuttingelement positioned in an arm body of the milling arm and rotatable abouta rotational axis, and at least one fixed cutting element positioned inthe arm body of the milling arm.
 13. The milling tool of claim 12, therotational axis being non-parallel to the cutting direction.
 14. Themilling tool of claim 12, the rotational axis being oriented at adeclination from the cutting direction between 0° and 45°.
 15. Themilling tool of claim 14, the rotatable cutting element having a bevelthat is complimentary to the declination.
 16. The milling tool of claim12, the rotational axis being oriented radially outward from the cuttingdirection at a radial angle between 0° and 45°.
 17. The milling tool ofclaim 16, the rotatable cutting element having a bevel that iscomplimentary to the radial angle.
 18. The milling tool of claim 12, theplurality of milling arms being deployable from the body.
 19. A millingtool, the milling device comprising: a milling tool body; and aplurality of milling arms projecting radially from the body andconfigured to move about the milling tool body in a cutting direction,at least one milling arm of the plurality of milling arms including, arotatable cutting element positioned in an arm body of the milling armand rotatable about a rotational axis, at least one inside fixed cuttingelement fixed relative to the arm body and positioned in a downholedirection of the rotatable cutting element, and at least one outsidefixed cutting element fixed relative to the arm body and positionedradially outside of the at least one inside cutting element with asacrificial region positioned therebetween.
 20. The milling tool ofclaim 19, the at least one outside cutting element positioned at aradial end of the arm body.